1. Field of the Invention
The present invention relates to a semiconductor device. More particularly, the present invention relates to a CMOS image sensor capable of preventing scum formation and overlapping of neighboring color filters. A method for fabricating the same is also disclosed.
2. Description of the Prior Art
As is well known, an image sensor is an apparatus for sensing a light beam reflected from an object to generate an image data. Especially, an image sensor fabricated by using a complementary metal oxide semiconductor (CMOS) technology is called a CMOS image sensor.
Generally, the CMOS image sensor includes a plurality of unit pixels. Each of the unit pixels also includes a light sensing element and a plurality of transistors. The light sensing element such as a photodiode senses incident light beam to generate photoelectric charges corresponding to an amount of the incident light beam. The transistors perform switching operations to control a transfer of the photoelectric charges.
FIG. 1 is a circuit diagram showing a unit pixel contained in a CMOS image sensor. Here, a reference symbol ML denotes a load transistor for controlling a current that flows via an output node NO of the unit pixel 10.
Referring to FIG. 1, the unit pixel 10 includes a photodiode 12 and four transistors. Four transistors also include a transfer transistor MT, a reset transistor MR, a drive transistor MD and a select transistor MS.
The photodiode 12 senses an incident light to generate photoelectric charges. The transfer transistor MT, coupled between the photodiode 12 and a sensing node NS, transfers the photoelectric charges to the sensing node NS. The reset transistor MR, coupled between a power terminal VDD and the sensing node NS, transfers a reset voltage level from a voltage source to the photodiode 12 and the drive transistor MD.
The drive transistor MD, whose drain is coupled to the power terminal VDD, amplifies a voltage level of the sensing node NS to output an amplified signal. The select transistor MS, coupled between the drive transistor MD and an output node NO, performs a switching operation to output the amplified signal as an image data via the output node NO.
FIG. 2 is a cross-sectional view showing a conventional CMOS image sensor.
As shown, a passivation layer 20 is formed on a semiconductor structure (not shown) including a photodiode and a peripheral circuit. Dyed photoresists are coated on the passivation layer 20 and then patterned to sequentially form color filters. However, due to an influence of the previously formed color filter, a scum is formed in the color filter and an overlap of neighboring color filters is occurred so that a sensitivity of the color filters is degraded.
A CMOS image sensor is disclosed for preventing a formation of scum and overlapping of neighboring color filters.
An image sensor is disclosed which comprises: a semiconductor structure; a first color filter formed on the semiconductor structure, wherein the first color filter includes a first stacked layer, the first stacked layer having a first nitride layer and a first oxide layer; a second color filter, wherein the second color filter is formed with a dyed photoresist and in contact with the first color filter; and a third color filter formed on a portion where is not overlapped with the first and the second color filter, wherein the third color filter includes a second stacked layer, the second stacked layer having a second nitride layer and a second oxide layer.
A method for fabricating an image sensor is also disclosed which comprises: a) providing a semiconductor structure; b) forming a first color filter on the semiconductor structure, wherein the first color filter includes a first stacked layer having a first nitride layer and a first oxide layer; c) forming a second color filter in contact with the first color filter; and d) forming a third color filter on a portion where is not overlapped with the first and the second color filter, wherein the third color filter includes a second stacked layer having a second nitride layer and a second oxide layer.